Calculate fines in days debarred RFC

Koha 3.0 lets the library define fines in money only. Some libraries needs to be able to set “debarred” fines. When a patron returns books lately, he is debarred for some days. The debar-fines will require :

• addition of a new field in patrons table, enddebardate, that is filled with the end of the debarring.
• the debar status will still be set by overdue rules.
• when the patron returns the book, if the fines are set to “days”, then Koha will calculate how long the patron is debarred. X = today - returndate - grace time. The patron is then debarred and the enddebardate is set.
• Calculation of the enddebardate. How the end of the debar date is calculated depends on a syspref too. It can be debardate = debardate+X (debarment cumulative), or debardate = max(debardate,today+X) (debarment not cumulative)